Internal combustion engines, in particular internal combustion engines that are used in motor vehicles may be equipped with a fuel injection system. In particular in the case of gasoline injection for applied-ignition engines, a distinction is made between intake pipe injection (also referred to as port injection), in which the injection valve is situated in the intake pipe upstream of an inlet valve of the respective cylinder, and direct injection, in which the fuel is injected directly into the cylinder. Intake pipe injection permits simple production of a homogeneous fuel-air mixture which is introduced into the combustion chamber of the cylinder.
Direct injection may permit different forms of combustion. Firstly, it is possible for a stratified charge to be produced in the combustion chamber of the cylinder, whereby the engine may, in the part-load range, be operated with high efficiency with a “lean” mixture. Secondly, it is also possible for a homogeneous fuel-air mixture to be produced in the combustion chamber, which may be optimal in the full-load range. To permit both combustion with a stratified “lean” mixture and also with a homogeneous mixture, complex interaction is required between the injection nozzle, the geometry of the combustion chamber, the location of the ignition spark and the flow of the gas introduced into the combustion chamber. As a result of realizing different forms of combustion, internal combustion engines with direct injection may more efficiently utilize fuel. A motor vehicle operated using an internal combustion engine with direct injection therefore may exhibit lower fuel consumption than a motor vehicle with a corresponding internal combustion engine with intake pipe injection.
At the transition between the different forms of combustion that may be realized by a direct injection device, provision may be made to ensure the stability of the combustion. Furthermore, different forms of combustion may keep the particle formation in the exhaust gas adequately low both with regard to soot mass and soot particle count such that no particle filter may be used in order to adhere to the applicable exhaust-gas regulations. For this purpose, it is known to provide not only the injection system for the direct injection into the combustion chamber but also a further injection system for an intake pipe injection. A combination of intake pipe injection and direct injection may make it possible to ensure both the stability of the combustion and also an adequate suppression of the soot formation in the exhaust gas. Owing to the plurality of injection systems, however, such a combination of intake pipe injection and direct injection may involve considerable outlay.
It is also known, in order to reduce fuel consumption in the part-load range, for individual cylinders to not be utilized for power generation (selective cylinder deactivation). U.S. 2005/0011485 A1 describes a heavy-duty engine in which, at low load, cylinders can be selectively deactivated. To avoid pumping losses, the inlet valve and the outlet valve of a deactivated cylinder remain closed. This does not permit an adequate reduction of soot formation with simultaneously efficient fuel utilization in different load ranges.
The inventors herein recognize the abovementioned disadvantages and disclose a system and method for the reduction of pumping losses and soot formation with selective cylinder deactivation. A four-stroke internal combustion engine which is operated or controlled in accordance with the disclosure has a multiplicity of cylinders, a fuel direct injection device and a selective cylinder deactivation device. The internal combustion engine is in particular an applied-ignition engine. The internal combustion engine has an injection system which, for each cylinder, comprises at least one injection nozzle for the direct injection of fuel into the combustion chamber of the respective cylinder. The injection system may furthermore comprise one or more injection pumps and corresponding lines and a controller for the control of the injection valves and of the pump or pumps. The internal combustion engine furthermore has a selective cylinder deactivation device, and it is thus possible for one or more cylinders to not be utilized for power generation in the part-load range; the fuel consumption of the internal combustion engine in the part-load range can thus be reduced. It is in particular the case that the injection system is correspondingly designed for realizing the selective cylinder deactivation.
According to the disclosure, in a load transition range of the internal combustion engine, during a compression stroke of a first cylinder which is not utilized for power generation, that is to say which is “deactivated”, fuel is injected into a combustion chamber of the first cylinder. The load transition range is in particular a medium-load range which is passed through upon the transition from a part-load range to a full-load range of the internal combustion engine or, conversely, from a full-load range to a part-load range of the internal combustion engine. The injection of fuel takes place in particular during a time period which is short in relation to the duration of the compression stroke, that is to say in relation to the duration of the upward movement of the piston, and said injection of fuel may for example take the form of a main injection or be similar to a main injection of an injection process broken down into multiple partial injections.
Furthermore, according to the disclosure, an inlet valve of the first cylinder is open during the compression stroke in order to make the fuel-air mixture produced by the fuel injection available to a second cylinder, which is utilized for power generation and which is thus not deactivated, for the intake or charge of the combustion chamber of the second cylinder. For this purpose, the inlet valve is open for a period of time which is at least partially subsequent to the fuel injection. The mixture produced by the fuel injection, in particular a fuel-air mixture composed of the air supplied into the combustion chamber and the fuel injected into said combustion chamber, can therefore pass into an intake tract of the internal combustion engine and out of said intake tract into the second cylinder which is utilized for power generation. Within the context of the present disclosure, “intake tract” refers to a region of the internal combustion engine from which the second cylinder is filled with gas, in particular an intake manifold or an intake pipe of the second cylinder. In the case of a supercharged engine, the intake tract may be at elevated pressure, and if an exhaust-gas recirculation system is provided, it may also be possible for a mixture of air and recirculated exhaust gas to be available in the intake tract for the charging of the cylinders. The first cylinder may also be charged from the intake tract. As a result of the compression movement of the piston of the first cylinder, the mixture is forced out of the combustion chamber of the first cylinder into the intake tract and onward into the combustion chamber of the second cylinder. Here, the second cylinder may be operated in the normal mode and thereby contributes to the generation of the mechanical power of the internal combustion engine and to the drive of the first cylinder which is not utilized for power generation. Since the first cylinder is deactivated, the mixture produced in the first cylinder is not ignited, and it is preferably the case that no further injection takes place during the compression stroke after the closing of the inlet valve. The internal combustion engine may comprise further cylinders which can be deactivated or utilized for power generation.
By virtue of the fact that, during a compression stroke of a cylinder which is not utilized for power generation, an injection of fuel takes place into a combustion chamber of the cylinder and an inlet valve of the cylinder is open for the purpose of making the mixture produced therein available to a further cylinder which is utilized for power generation and which is in particular operated in the normal mode, it is made possible for an already substantially homogeneous mixture to be introduced into the second cylinder, into which mixture a further injection of fuel may take place if appropriate. In this way, it is possible both for the stability of the combustion to be increased and also for the soot generation to be reduced, without an intake pipe injection device having a dedicated injection valve or injection system. In this way, it is made possible in a simple manner to increase the quality of the combustion and in particular the exhaust-gas quality, while realizing efficient fuel utilization. According to the disclosure, therefore, selective cylinder deactivation and variable inlet valve actuation are combined with one another to attain the advantages of selective cylinder deactivation with regard to fuel consumption but also to permit the operation of the non-deactivated cylinders with reduced soot formation.
A system is disclosed for a four-stroke internal combustion engine comprising: at least two cylinders; a fuel direct injection device; a variable valve timing system; an engine controller to control valve timing according to load; wherein, below a lower load threshold, a first cylinder is deactivated, an injection of fuel takes place into a combustion chamber of the first cylinder and an inlet valve of the first cylinder is open during a compression stroke. The opening of the inlet valve during a compression stroke of the first cylinder when deactivated allows the substantially homogenous air-fuel mixture therein to escape into the intake manifold and be made available to the second and active cylinder.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Further, the inventors herein have recognized the disadvantages noted herein, and do not admit them as known.